Vertebral fractures in humans are associated with significant morbidity and mortality. Particularly, there is a relatively high prevalence of osteoporotic vertebral compression fractures (VCFs) in the elderly population, and especially in older women (i.e., aged 50 or older). VCFs are also common in patients on long-term steroid therapy, and in those suffering from multiple myeloma or cancers that have metastasized to the spine. Medical treatment of these fractures may include bed rest, orthotics, and analgesic medications. VCFs can also be caused by trauma, such as an automobile accident or falls. Medical treatment for traumatic fractures may include fusions and fixation with screws, rods and plates.
Vertebroplasty is a procedure in which bone cement is injected into a fractured vertebral body in an attempt to stabilize fractured segments and reduce pain. This procedure was originally used to treat spinal lesions caused by metastases and has recently been used to treat severe bone loss caused by osteoporosis (Eck et al. (Mar. 2002) American J Orthop. 31(3):123-127).
Percutaneous vertebroplasty (PVP) consists of percutaneous injection of a material, such as polymethylmethacrylate, into the fractured vertebral body to produce stability and pain relief. In fact, biomechanical testing has shown that PVP can restore strength and stiffness of the vertebral body to the pre-fracture levels. Moreover, clinical results have indicated some immediate and maintained pain relief in 70-95% of the patients. However, there may be complications which include cement extravasation into the spinal canal or into the venous system.
Kyphoplasty is a new technique, which introduces an expandable body into the vertebral body to reduce the VCF while creating a cavity for the cement injection. This technique has the benefit of sustained vertebral body height restoration and angular deformity correction as well as low pressure delivery of the cement resulting in less extravasation of the cement. Research continues into the development of injectable materials that are resorbable and allow for new bone formation.
Although, vertebroplasty and kyphoplasty are effective in the treatment of osteoporotic VCFs, there is a continuous need for new materials and methods that may allow for a faster return to function and otherwise improve all forms of such medical treatment.
Many bone cements and fillers comprise two components which must be mixed immediately prior to use, often being combined in a syringe just before or during injection. Exemplary syringe systems for injecting such two component materials are shown in copending U.S. application Ser. No. 10/660,465, filed on Sep. 10, 2003, the full disclosure of which is incorporated herein by reference. The need to mix component materials immediately prior to use can complicate the application of such bone filler materials (see U.S. Pat. No. 6,652,887). For example, the mixing of components according to specific protocols can introduce errors prior to injection (e.g., errors in timing, errors in measurement, etc.). Furthermore, the workability or handling characteristics of materials that require mixing is usually fairly short (e.g., less than 30 minutes) once the materials have been combined. Hence, there is a need in the art to provide simpler and improved forms of bone substitute materials which are pre-mixed, pre-filled, ready-for-use, and exhibit an extended workability without the loss of potency. The instant invention addresses this need.